/* in_cksum.c * 4.4-Lite-2 Internet checksum routine, modified to take a vector of * pointers/lengths giving the pieces to be checksummed. * * $Id: in_cksum.c 12117 2004-09-28 00:06:32Z guy $ */ /* * Copyright (c) 1988, 1992, 1993 * The Regents of the University of California. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)in_cksum.c 8.1 (Berkeley) 6/10/93 */ #ifdef HAVE_CONFIG_H # include "config.h" #endif #include <glib.h> #include <epan/in_cksum.h> /* * Checksum routine for Internet Protocol family headers (Portable Version). * * This routine is very heavily used in the network * code and should be modified for each CPU to be as fast as possible. */ #define ADDCARRY(x) (x > 65535 ? x -= 65535 : x) #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);} int in_cksum(const vec_t *vec, int veclen) { register const guint16 *w; register int sum = 0; register int mlen = 0; int byte_swapped = 0; union { guint8 c[2]; guint16 s; } s_util; union { guint16 s[2]; guint32 l; } l_util; for (; veclen != 0; vec++, veclen--) { if (vec->len == 0) continue; w = (const guint16 *)vec->ptr; if (mlen == -1) { /* * The first byte of this chunk is the continuation * of a word spanning between this chunk and the * last chunk. * * s_util.c[0] is already saved when scanning previous * chunk. */ s_util.c[1] = *(const guint8 *)w; sum += s_util.s; w = (const guint16 *)((const guint8 *)w + 1); mlen = vec->len - 1; } else mlen = vec->len; /* * Force to even boundary. */ if ((1 & (unsigned long) w) && (mlen > 0)) { REDUCE; sum <<= 8; s_util.c[0] = *(const guint8 *)w; w = (const guint16 *)((const guint8 *)w + 1); mlen--; byte_swapped = 1; } /* * Unroll the loop to make overhead from * branches &c small. */ while ((mlen -= 32) >= 0) { sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7]; sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11]; sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15]; w += 16; } mlen += 32; while ((mlen -= 8) >= 0) { sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; w += 4; } mlen += 8; if (mlen == 0 && byte_swapped == 0) continue; REDUCE; while ((mlen -= 2) >= 0) { sum += *w++; } if (byte_swapped) { REDUCE; sum <<= 8; byte_swapped = 0; if (mlen == -1) { s_util.c[1] = *(const guint8 *)w; sum += s_util.s; mlen = 0; } else mlen = -1; } else if (mlen == -1) s_util.c[0] = *(const guint8 *)w; } if (mlen == -1) { /* The last mbuf has odd # of bytes. Follow the standard (the odd byte may be shifted left by 8 bits or not as determined by endian-ness of the machine) */ s_util.c[1] = 0; sum += s_util.s; } REDUCE; return (~sum & 0xffff); } /* * Given the host-byte-order value of the checksum field in a packet * header, and the network-byte-order computed checksum of the data * that the checksum covers (including the checksum itself), compute * what the checksum field *should* have been. */ guint16 in_cksum_shouldbe(guint16 sum, guint16 computed_sum) { guint32 shouldbe; /* * The value that should have gone into the checksum field * is the negative of the value gotten by summing up everything * *but* the checksum field. * * We can compute that by subtracting the value of the checksum * field from the sum of all the data in the packet, and then * computing the negative of that value. * * "sum" is the value of the checksum field, and "computed_sum" * is the negative of the sum of all the data in the packets, * so that's -(-computed_sum - sum), or (sum + computed_sum). * * All the arithmetic in question is one's complement, so the * addition must include an end-around carry; we do this by * doing the arithmetic in 32 bits (with no sign-extension), * and then adding the upper 16 bits of the sum, which contain * the carry, to the lower 16 bits of the sum, and then do it * again in case *that* sum produced a carry. * * As RFC 1071 notes, the checksum can be computed without * byte-swapping the 16-bit words; summing 16-bit words * on a big-endian machine gives a big-endian checksum, which * can be directly stuffed into the big-endian checksum fields * in protocol headers, and summing words on a little-endian * machine gives a little-endian checksum, which must be * byte-swapped before being stuffed into a big-endian checksum * field. * * "computed_sum" is a network-byte-order value, so we must put * it in host byte order before subtracting it from the * host-byte-order value from the header; the adjusted checksum * will be in host byte order, which is what we'll return. */ shouldbe = sum; shouldbe += g_ntohs(computed_sum); shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); return shouldbe; }

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